A toll of that magnitude would push to over 1,500 the number of people who have died so far this year after being packed into rickety boats by human traffickers to cross the Mediterranean in a bid to reach a better life in Europe.

The Italian coast guard said just 28 people had been saved from where the ship sank, 70 miles off the coast of Libya.

These small numbers make more sense if hundreds of people were locked in the hold, because with so much weight down below, "surely the boat would have sunk," said Gen. Antonino Iraso, of the Italian Border Police, which has deployed boats in the operation.

Prosecutor Giovanni Salvi said that a survivor from Bangladesh described the situation on the fishing boat to prosecutors who interviewed him in a hospital.

The man said about 300 people were in the hold, locked in there by the smugglers, when the vessel set out. He said that of the 950 who set out aboard the doomed boat, some 200 were women and several dozen were children.

Salvi stressed that there was no confirmation yet of the man's account and that the investigation was ongoing.

Meanwhile, Italian Premier Matteo Renzi will ask his EU counterparts to confront instability in Libya more decisively, but he ruled out ground troops.

"At this moment to intervene with international forces on the ground is a risk that is absolutely excessive," Renzi said. "We cannot think about sending tens of thousands of men without a strategy, on a wave of emotion."

Renzi said he would ask his European counterparts to participate in a joint operation targeting smugglers. He said that Italy has so far arrested nearly 1,000, but needs help.

EU foreign ministers are meeting in Luxembourg today focusing on the migration crisis and the role of the conflict in Libya fueling the influx.

The EU's top migration official, Dimitris Avramopoulos, has canceled a trip to the Spanish enclaves of Ceuta and Melilla to attend.

Fighting in Libya has escalated to its worst levels since the 2011 civil war that ended with the overthrow and killing of longtime dictator Moammar Gadhafi.

The country now has rival governments - the internationally recognized one in the eastern city of Tobruk, and an Islamist-backed one in the capital, Tripoli. The two sides have been negotiating in Morocco to end the fighting.

missing

Malta and Italy are closest to the Libyan coast, and have received the brunt of a migrant tide that carried 219,000 people from Africa to Europe last year. Some 3,500 died or went missing along the way.

Malta's Prime Minister Joseph Muscat said on Monday the United Nations should mandate a force to intervene directly in Libya to disrupt or attack the traffickers and stop the boats from setting off.

Before Sunday's disaster, the International Organisation for Migration estimated around 20,000 migrants had reached the Italian coast this year, and 900 had died.